Fabrication tolerance of Ti:LiNbO₃ waveguides

The tolerance of waveguide designs to the cutoff condition has been studied. To make single-mode waveguides, the width, thickness of the Ti stripe before diffusion, diffusion conditions, and operating wavelength are usually chosen empirically. The cutoff wavelengths of the fundamental mode and the first-order mode were calculated using the 3-D beam propagation method. Cutoff wavelengths of the first-order mode calculated directly from design parameters and fabrication conditions are shown along with measured results; the agreement is good. The calculated thickness of Ti needed to support the fundamental (lower group of curves) and first-order mode (upper group of curves) for Ti stripe widths of 6, 7, and 8 μm is also shown.